Technical Field
The present disclosure relates to a spark plug for an internal combustion engine.
Description of the Related Art
As an ignition means of an internal combustion engine such as an engine of a vehicle, a spark plug has been used. Such a spark plug is configured to have a center electrode, a ground electrode and a discharge gap therebetween, where discharge is produced at the discharge gap. Sparks caused by the discharge make thermal contact with an air fuel mixture in the combustion chamber, thereby igniting the mixture in the combustion chamber.
For example, Japanese Patent Application Laid-Open Publication No. 2013-161523 discloses a spark plug having a plurality of ground electrodes to provide a plurality of discharge gaps. This spark plug produces a primary discharge at a discharge gap provided in the upstream side of the mixture in the combustion chamber, among the plurality of discharge gaps, thereby causing a primary plasma. The primary plasma flows together with an air fuel mixture stream in the combustion chamber and flows into the discharge gap located in the downstream side. The primary plasma flows into the discharge gap, thereby prompting occurrence of discharge at the discharge gap in the downstream side.
However, according to the spark plug disclosed in the above-mentioned patent literature, for example, in an environment where the air flow is likely to be faster in the combustion chamber due to a tumble engine or the like, it is difficult to have a primary plasma produced in the primary discharge gap in the upstream side stably flow into the discharge gap in the downstream side. Hence, it is considered that the spark plug according to the above-mentioned patent literature has to be improved in view of ignitability of the air fuel mixture.